Sorting a large dataset is a problem commonly found in many applications. The total time required to sort a large dataset can be split into two parts: first, the input/output (I/O) delay in reading all the unsorted data from stable storage (e.g., disk) and writing the sorted data back. Second, there are CPU requirements for comparing enough of the data elements sufficiently to sort them.
The I/O portion of the sorting process is typically much slower than computation, particularly if the amount of computation done per unit of data is small. The time to sort data tends to be dominated by the time it takes to read or write the data from or to either the network or the storage medium (e.g. disk). This has changed in some recent storage systems, where I/O is dramatically faster than in previous systems—often by an order of magnitude. When sorting is implemented on such systems, the time required for computation becomes more significant, and it becomes more significant to optimize this portion of the sorting process.